An approach for heat dissipation in integrated circuit devices is provided. A method includes forming an isolation layer on an electrically conductive feature of an integrated circuit device. The method also includes forming an electrically conductive layer on the isolation layer. The method additionally includes forming a plurality of nanowire structures on a surface of the electrically conductive layer.
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1. A method, comprising:
forming a plurality of nanowire structures on a surface of an electrically conductive layer by applying an electric potential to the electrically conductive layer through a wiring path;
forming a discontinuity in the wiring path after the plurality of nanowire structures are formed; and
depositing an insulator layer over the plurality of nanowire structures so as to cover a top surface of the plurality of nanowire structures with the insulator layer, wherein before the forming the plurality of nanowire structures, a barrier layer is formed on an entire surface of a semiconductor structure, the method further comprising:
etching a portion of the barrier layer on a drain region of the semiconductor structure;
depositing an isolation layer on the drain region; and
depositing the electrically conductive layer on the isolation layer.
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submerging at least the electrically conductive layer in a growth solution comprising a zinc source; and
applying an electric potential between a first electrode wired to the electrically conductive layer and a second electrode submerged in the growth solution.
11. The method of
the electrically conductive layer comprises silicide; and
the forming the plurality of nanowire structures comprises growing a plurality of spaced apart ZnO columnar structures on the silicide using an electrochemical deposition process.
12. The method of
13. The method of
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15. The method of
16. The method of
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The present invention relates to integrated circuits and, more particularly, to methods and systems for dissipating heat in integrated circuit devices.
Silicon-on-insulator is the process of fabricating silicon based devices, such as complementary metal oxide semiconductor (CMOS) field effect transistors (FET) on top of a layer of electrically insulating material, such as an oxide. The layer of oxide is on top of a bulk silicon substrate in an integrated circuit (IC) chip and acts as an electrical barrier between the devices (e.g., FETs) and the bulk silicon. The layer of oxide greatly reduces electrical leakage from the devices, but also greatly reduces heat flow away from these devices. Accumulation of heat within a device, such as a FET, can reduce the performance and/or useful lifetime of the device.
Heat generation is a limiting factor to improving device operation in many technologies. For example, in radio frequency (RF) CMOS, switch performance is severely limited by the heat generated by the switch at high frequency. RF switches can use 200-300 mW of power, while an RF amplifier can use up to 3 W of power. This large amount of current flow over a relatively small region can result in heating of the devices up to 200° C. in the case of an RF amplifier. These elevated temperatures can significantly change the characteristics of the devices, as well as degrade the integrity of its construction materials. Since many of these devices are now built on SOI, the primary path for drawing heat away from the devices is through the electrical contacts formed over the devices. Further amplifying this problem is the desire to remove or reduce the number of electrical contacts in order to lower the capacitance of the devices, which will increase the need to dissipate heat because the electrical contacts do provide a path for the heat to escape. The RF parts affected by this issue are largely in cellular telephones.
Similar heat-related issues are present in the bipolar junction transistor (BJT) devices that are commonly used in radar and collision avoidance. SiGe-based BJT devices are driving toward increased operating frequencies of up to 300 GHz. As this frequency increases, the trapped residual heat plays a more prevalent role in degrading device performance. Passive structures, such as resistors, are also negatively affected by excess heat, which can affect the temperature coefficient of resistance.
In a first aspect of the invention, a method of manufacturing a semiconductor structure includes forming an isolation layer on an electrically conductive feature of an integrated circuit device, wherein the isolation layer is electrically insulating and thermally conducting. The method also includes forming an electrically conductive layer on the isolation layer. The method additionally includes forming a plurality of nanowire structures on a surface of the electrically conductive layer.
In another aspect of the invention, a method of manufacturing a semiconductor structure includes forming an isolation layer on an electrically conductive feature of an integrated circuit device. The method includes forming an electrically conductive layer on the isolation layer. The method also includes forming a plurality of nanowire structures on a surface of the electrically conductive layer. The isolation layer is formed to electrically isolate the electrically conductive feature from the electrically conductive layer. The plurality of nanowire structures are formed of a high thermal conductivity material that provides a heat path away from the electrically conductive feature.
In yet another aspect of the invention, a semiconductor structure includes: an isolation layer on an electrically conductive feature of an integrated circuit device; an electrically conductive layer on the isolation layer; and a plurality of nanowire structures on a surface of the electrically conductive layer. The isolation layer electrically isolates the electrically conductive feature from the electrically conductive layer. The plurality of nanowire structures are composed of a high thermal conductivity material that provides a heat path away from the electrically conductive feature.
In another aspect of the invention, a design structure tangibly embodied in a machine readable storage medium for designing, manufacturing, or testing an integrated circuit is provided. The design structure comprises the structures of the present invention. In further embodiments, a hardware description language (HDL) design structure encoded on a machine-readable data storage medium comprises elements that when processed in a computer-aided design system generates a machine-executable representation of a semiconductor structure with nanowires which comprises the structures of the present invention. In still further embodiments, a method in a computer-aided design system is provided for generating a functional design model of the semiconductor structure with nanowires. The method comprises generating a functional representation of the structural elements of the semiconductor structure with nanowires.
The present invention is described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention.
The invention relates to integrated circuits and, more particularly, to methods and systems for dissipating heat in integrated circuit devices. According to aspects of the invention, nanowire structures are formed to produce an electrically isolated but thermally conductive path for heat to diffuse away from a device. By placing nanowires on and near devices, the nanowires provide a path for heat dissipation and/or heat transport from a source to a sink, and drastically cool the device, which improves device performance. In embodiments, the nanowires comprise zinc oxide (ZnO), which provides the benefit that the nanowires are easily formed with high selectivity via an electrochemical hydrothermal bath. In addition, ZnO has a high thermal conductivity and is a cost-effective, environmentally friendly, and readily available material. Including these nanowire heat fins in devices as described herein provides for further optimization of devices, such as reducing the number of contacts to lower the capacitance of RF devices.
Implementations of the invention include providing an electrically isolated but thermally conductive path for heat to diffuse away from the device. Such heat removal allows the device to operate with increased performance and reduces the likelihood of heat-related materials degradation. Embodiments include growing ZnO nanowires on top of a conductive material (e.g., silicide) that is deposited on top of an electrical isolation layer above the device. The pads and wiring used in the nanowire deposition may also be used for heat conduction from the nanowire arrays to the metal pads.
The semiconductor structures of the present invention can be manufactured in a number of ways using a number of different tools. In general, and unless otherwise noted herein, the methodologies and tools are used to form structures with dimensions in the micrometer scale. The methodologies, i.e., technologies, employed to manufacture the semiconductor structures of the present invention have been adopted from integrated circuit (IC) technology. For example, the structures of the present invention are built on wafers and are realized in films of material patterned by photolithographic processes on the top of a wafer. In particular, the fabrication of the semiconductor structures of the present invention may use three basic building blocks: (i) deposition of thin films of material on a substrate, (ii) applying a patterned mask on top of the films by photolithographic imaging, and (iii) etching the films selectively to the mask.
The constituent materials of the SOI wafer 10 may be selected based on the desired end use application of the semiconductor device. For example, the substrate 15 may be composed of any suitable material including, but not limited to, Si, SiGe, SiGeC, SiC, GE alloys, GaAs, InAs, InP, and other III/V or II/VI compound semiconductors. The buried insulator layer 20 may be composed of oxide, such as SiO2, and may be referred to as a buried oxide (BOX) layer 20. Moreover, although the SOI wafer is referred to as “silicon on insulator,” the semiconductor layer 25 is not limited to silicon. Instead, the semiconductor layer 25 may be comprised of various semiconductor materials, such as, for example, Si, SiGe, SiC, SiGeC, etc.
In embodiments, the SOI wafer 10 has a thickness of about 700 μm, with the BOX layer 20 having a thickness in a range of about 0.1 μm to about 2 μm, and the semiconductor layer 25 having a thickness in a range of about 0.1 μm to about 0.2 μm. However, the invention is not limited to these dimensions, and the various portions of the SOI wafer may have any desired thicknesses based upon the intended use of the final semiconductor device.
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In embodiments, the nanowires 140 comprise zinc oxide (ZnO) and are formed with high selectivity using an electrochemical hydrothermal bath. ZnO is a semiconductor material having a high thermal conductivity of about 135 W/(m·K). An exemplary process for forming the nanowires 140 includes providing a solution comprising a 1:1 mixture of 0.025 M zinc nitrate hexahydrate (Zn(NO3)2.6H2O) and 0.025 M hexamethylenetetramine (HMTA, C6H2N4) in deionized water. The solution is stirred and heated to about 90° C. The wafer is suspended in the solution at this temperature with the growth surface (i.e., the exposed conducting layer 130) facing downward. A first electrode of an external voltage application circuit is connected through wiring in the wafer 10 to the conducting layer 130, and a second electrode of the external voltage application circuit is suspended in the solution. The external voltage application circuit applies a potential of about 1 V to 5 V between the first electrode and the second electrode while the growth surface is submerged in the solution. Under these conditions, the nanowires 140 grow as spaced apart columnar structures on the growth surface via an electrochemical deposition process. The invention is not limited to forming the nanowires 140 using an electrochemical deposition process, and instead the nanowires 140 may be formed using any suitable formation process.
The voltage and amount of time applying the voltage in solution may be used to control the height and width of the nanowires 140. In one example, each one of the nanowires 140 is grown to a nominal height “h” of about 1700 nm and a nominal width “w” of about 240 nm using a voltage of 2.5 V and a growth time of 60 minutes. In one example, each one of the nanowires 140 is grown to a nominal height of about 3000 nm and a nominal width of about 640 nm using a voltage of 2.5 V and a growth time of 120 minutes. Height of the nanowires 140 is measured as the extent of growth outward from the growth surface, e.g., the exposed surface of the conducting layer 130. As used herein, nanowire and nanowire structure refer to a columnar structure having a sub-micron width. The invention is not limited to these values, and one or more of the parameters of the growth process (e.g., constituents of the solution, temperature, voltage potential, growth time, etc.) may be tailored to achieve a desired nanowire structure according to aspects of the invention.
In aspects, the nanowires 140′ on the source region 85a and the nanowires 140 on the drain region 85b are formed simultaneously. For example, a conducting layer similar to conducting layer 130 may be formed on the second portion of source region 85a at the same time and in the same manner of formation as conducting layer 130 using appropriate mask patterns. In this manner, nanowires 140 and 140′ are grown at the same time using the electrochemical deposition process described herein. Similarly, the contacts 205 and 205′ may be formed simultaneously using the processes described with respect to
Design flow 900 may vary depending on the type of representation being designed. For example, a design flow 900 for building an application specific IC (ASIC) may differ from a design flow 900 for designing a standard component or from a design flow 900 for instantiating the design into a programmable array, for example a programmable gate array (PGA) or a field programmable gate array (FPGA) offered by Altera® Inc. or Xilinx® Inc.
Design process 910 preferably employs and incorporates hardware and/or software modules for synthesizing, translating, or otherwise processing a design/simulation functional equivalent of the components, circuits, devices, or logic structures shown in
Design process 910 may include hardware and software modules for processing a variety of input data structure types including netlist 980. Such data structure types may reside, for example, within library elements 930 and include a set of commonly used elements, circuits, and devices, including models, layouts, and symbolic representations, for a given manufacturing technology (e.g., different technology nodes, 32 nm, 45 nm, 90 nm, etc.). The data structure types may further include design specifications 940, characterization data 950, verification data 960, design rules 970, and test data files 985 which may include input test patterns, output test results, and other testing information. Design process 910 may further include, for example, standard mechanical design processes such as stress analysis, thermal analysis, mechanical event simulation, process simulation for operations such as casting, molding, and die press forming, etc. One of ordinary skill in the art of mechanical design can appreciate the extent of possible mechanical design tools and applications used in design process 910 without deviating from the scope and spirit of the invention. Design process 910 may also include modules for performing standard circuit design processes such as timing analysis, verification, design rule checking, place and route operations, etc.
Design process 910 employs and incorporates logic and physical design tools such as HDL compilers and simulation model build tools to process design structure 920 together with some or all of the depicted supporting data structures along with any additional mechanical design or data (if applicable), to generate a second design structure 990.
Design structure 990 resides on a storage medium or programmable gate array in a data format used for the exchange of data of mechanical devices and structures (e.g. information stored in a IGES, DXF, Parasolid XT, JT, DRG, or any other suitable format for storing or rendering such mechanical design structures). Similar to design structure 920, design structure 990 preferably comprises one or more files, data structures, or other computer-encoded data or instructions that reside on transmission or data storage media and that when processed by an ECAD system generate a logically or otherwise functionally equivalent form of one or more of the embodiments of the invention shown in
Design structure 990 may also employ a data format used for the exchange of layout data of integrated circuits and/or symbolic data format (e.g. information stored in a GDSII (GDS2), GL1, OASIS, map files, or any other suitable format for storing such design data structures). Design structure 990 may comprise information such as, for example, symbolic data, map files, test data files, design content files, manufacturing data, layout parameters, wires, levels of metal, vias, shapes, data for routing through the manufacturing line, and any other data required by a manufacturer or other designer/developer to produce a device or structure as described above and shown in
The methods as described above are used in the fabrication of integrated circuit chips. The resulting integrated circuit chips can be distributed by the fabricator in raw wafer form (that is, as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case the chip is mounted in a single chip package (such as a plastic carrier, with leads that are affixed to a motherboard or other higher level carrier) or in a multichip package (such as a ceramic carrier that has either or both surface interconnections or buried interconnections). In any case, the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) an end product. The end product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor.
The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
van Kessel, Theodore G., Wolf, Randy L., Botula, Alan B., Slinkman, James A., Lifson, Max L.
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